Tonofilament protein from newborn rat epidermis. Isolation, localization, and biosynthesis of marker of epidermal differentiation.

A novel extraction procedure, previously used on the cell walls of dermatophytes, has been applied to the epidermis of newborn rat. A leucine-rich fraction was isolated which contained over 60% of the total epidermal radioactivity from [3H]leucine in 15 to 20% of the total protein. This fraction was further purified by chromatography in DEAE-cellulose and Sephadex G-200. The protein with the highest specific activity from [3H]leucine was isolated and gave a single band in sodium dodecyl sulfate polyacrylamide gels of molecular weight = 58,000. Antibody to this protein gave a single precipitin band by immunodiffusion and immunoelectrophoresis in agar with the purified protein. This antibody ultrastructurally immunolocalized specifically over tonofilaments in all layers of the epidermis, but showed no reaction in the dermis. The synthesis of this protein in vitro was inhibited by puromycin but not by actinomycin D, suggesting ribosomal synthesis involving a relatively long lived messenger.